Ruthenium(iv) oxide, RuO2 (CAS 12036-10-1), is a dark blue-black, rutile-structured oxide that is 75.9% ruthenium by weight and ranks as the most active oxygen-evolution electrocatalyst known. Industry supplies it mainly as an electrodeposited or thermally-formed coating on titanium for chlor-alkali anodes, not as a bulk commodity powder. Its identity, crystal structure, ruthenium content, physical properties, manufacture, industrial uses, commercial forms and hazard classification follow below, section by section.
What Is Ruthenium(iv) oxide?#
Ruthenium(iv) oxide is a binary oxide of the platinum group metal ruthenium, with the formula RuO2, CAS number 12036-10-1 and PubChem CID 82848. PubChem gives its molecular weight as 133.1 g/mol, lists the systematic name "dioxoruthenium," and assigns the InChIKey WOCIAKWEIIZHES-UHFFFAOYSA-N. Chemists and suppliers also call it ruthenium oxide or ruthenium dioxide, and it is cataloged among the platinum group metal compounds and catalysts on this site that carry a dedicated CAS registry entry.
| Property | Value |
|---|---|
| Preferred name | Ruthenium(iv) oxide |
| Alternate names | ruthenium oxide; ruthenium dioxide |
| CAS number | 12036-10-1 |
| PubChem CID | 82848 |
| PubChem IUPAC name | dioxoruthenium |
| InChIKey | WOCIAKWEIIZHES-UHFFFAOYSA-N |
| Molecular formula | O2Ru |
| Molecular weight | 133.1 g/mol |
| EC (EINECS) number | 234-840-6 |
Ruthenium is ruthenium (Ru), element 44, one of the six platinum group metals, and unlike many lighter transition metals it forms two commercially significant higher oxidation states, ruthenium(III) and ruthenium(IV); this oxide is the principal ruthenium(IV) representative.
Ruthenium(iv) oxide Structure and Bonding#
Ruthenium(iv) oxide adopts the rutile-type tetragonal structure, space group P42/mnm (No. 136), the same lattice type shared by titanium dioxide and several other platinum group metal dioxides. A 1997 neutron powder diffraction refinement in Acta Crystallographica Section B fixed the lattice constants at a = 4.4968(2) angstroms and c = 3.1049(1) angstroms, Z = 2; each ruthenium(IV) ion sits at the center of a distorted octahedron of six oxide ions, and each oxygen atom is coordinated trigonal-planar by three ruthenium atoms. That +4 state sits alongside ruthenium's other common state, +3, in the metal's own ruthenium electron configuration and oxidation states.
PGM Content of Ruthenium(iv) oxide#
Ruthenium(iv) oxide is 75.9% ruthenium by weight, a figure computed from the compound's own atomic composition rather than taken from a single reported number. Ruthenium's standard atomic weight is 101.07 g/mol, and the compound's molecular weight is 133.07 to 133.1 g/mol (PubChem CID 82848); dividing 101.07 by 133.07 gives 0.759, or 75.9 wt% ruthenium, with the remaining 24.1% accounted for by the two oxygen atoms in the formula O2Ru. That fraction is why a batch of RuO2, whether laboratory powder or bulk DSA coating material, tracks the ruthenium market rather than a flat per-gram specialty-chemical rate.
Physical and Chemical Properties#
Ruthenium(iv) oxide is a dark blue-black powder that is insoluble in water and in acids, dissolving only in molten alkali, and it decomposes rather than melting cleanly.
| Property | Value | Basis |
|---|---|---|
| Appearance | Dark blue-black powder | ChemicalBook aggregated technical data (single-source) |
| Decomposition/sublimation point | ~1200°C | ChemicalBook aggregated technical data (single-source) |
| Density | 6.97 g/cm3 at 25°C | ChemicalBook aggregated technical data (single-source) |
| Solubility | Insoluble in water and acids; soluble in molten alkali | ChemicalBook aggregated technical data (single-source) |
| Hygroscopicity | Hygroscopic | ChemicalBook aggregated technical data (single-source) |
| Crystal structure | Rutile-type tetragonal, space group P42/mnm (No. 136) | Acta Crystallographica B (1997) (single-source) |
| Magnetic behavior | +162.0e-6 cm3/mol molar susceptibility (paramagnetic) | Wikipedia (single-source) |
| Electrical resistivity | 35-40 microohm-cm at room temperature (well-crystallized thin film) | NSF PAR-hosted resistivity study (single-source) |
| Standard reduction potential | RuO2 + 4H+ + 2e- to Ru2+ + 2H2O, E° = +1.120 V | Wikipedia Standard Electrode Potential data page (Vanysek/CRC) |
| Standard reduction potential | RuO4 + 4H+ + 4e- to RuO2 + 2H2O, E° = +1.387 V | Wikipedia Standard Electrode Potential data page (Vanysek/CRC) |
For comparison, elemental ruthenium is far denser and more refractory than its dioxide; see ruthenium density and ruthenium melting point and boiling point for the metal's own values.
How Is Ruthenium(iv) oxide Made?#
Ruthenium(iv) oxide reaches most of its market as an electrode coating, formed by electrodepositing or thermally forming the oxide directly onto a titanium substrate rather than being cast or pressed from a pre-made powder. Sigma-Aldrich also sells a 99.9% trace-metals-basis powder grade, catalog number 238058, for research use, but the commercially larger volume is the electrodeposited or thermally-formed coating that supplies dimensionally stable anodes (DSA) to the chlor-alkali industry, per Sigma-Aldrich's listing and this site's catalysis research. No documented synthesis route for the standalone research-grade powder was found in the sources reviewed for this page; buyers sourcing bulk powder should confirm the route with the specific supplier.
What Is Ruthenium(iv) oxide Used For?#
Ruthenium(iv) oxide is used mainly as the active coating on dimensionally stable anodes (DSA) for industrial chlorine and oxygen-evolution electrolysis. RuO2 is, in fact, the most active oxygen-evolution (OER) electrocatalyst known, more active than iridium(IV) oxide on a thin-film basis, per a 2016 Catalysis Today study comparing Ru, RuO2, Ir and IrO2 electrodes. Under the strongly acidic, oxidizing conditions at a PEM (proton-exchange-membrane) electrolyzer anode, however, RuO2 corrodes to soluble, volatile ruthenium species, a stability failure rather than an activity shortfall, so iridium(IV) oxide, not RuO2, is the industry's PEM electrolyzer anode material despite ruthenium's higher intrinsic activity. RuO2's acidic-OER service is therefore confined to the milder conditions of chlor-alkali DSA anodes, where mixed RuO2/TiO2 (and RuO2-IrO2) coatings on titanium have displaced graphite anodes entirely.
RuO2 covers several further roles beyond electrolysis:
- Supercapacitor electrodes: hydrous RuO2 powder made by a sol-gel process and annealed at 150°C reached a peak specific capacitance of 720 F/g, a landmark 1995 Journal of the Electrochemical Society result still cited as a pseudocapacitor benchmark.
- Thick-film resistors and integrated circuits: RuO2's metallic-level electrical resistivity, 35 to 40 microohm-cm, makes it a standard resistive element in hybrid microelectronics.
- Cryogenic resistance thermometry: RuO2-based resistors serve as temperature sensors across roughly 0.02 K to 4 K.
- Sumitomo-Deacon HCl oxidation catalyst: RuO2 catalyzes the Deacon-type oxidation of hydrogen chloride to chlorine, recovering chlorine value from HCl byproduct streams.
Elemental ruthenium covers a wider set of applications; see ruthenium uses in industrial and automotive applications for the metal's full range.
Commercial Forms, Purity and Price#
The standard commercial grade of ruthenium(iv) oxide is a 99.9% trace-metals-basis powder, alongside the higher-volume electrodeposited or thermally-formed coating supplied directly onto titanium anode blanks.
| Grade | Form | Pack size class |
|---|---|---|
| Research/laboratory grade | 99.9% trace-metals-basis powder (Sigma-Aldrich 238058) | Milligram to multi-gram packs |
| Industrial DSA coating grade | Electrodeposited or thermally-formed RuO2, often as mixed RuO2/TiO2 or RuO2-IrO2 oxide coatings | Anode-blanket scale, sized to the electrolytic cell, not sold by weight of oxide alone |
Because the compound is 75.9% ruthenium by weight, buyers of bulk coating material effectively price it against contained ruthenium value rather than a flat per-gram catalog rate, the same logic applied across this site's other PGM compound pages. Current dealer-quoted pricing for the metal itself, not for RuO2, is tracked on DailyPlatinum's ruthenium price today page; ruthenium and the other minor PGMs trade on dealer quotes rather than a public exchange spot price.
Safety and Hazard Classification#
PubChem's aggregated Classification and Labelling Inventory record for ruthenium(iv) oxide, CID 82848, reports the GHS signal word Danger, mirroring notifications submitted to the European Chemicals Agency. Of the notifications aggregated, H272 (oxidizing solid, category 2) appears in 10.2%, H319 (serious eye irritation) in 40%, and H413 (long-lasting harm to aquatic life) in 35.9%, with Oxidizer and Irritant pictograms among the reported set. ChemicalBook's own aggregated safety data sheet, by contrast, records a lighter classification, signal word Warning with H319 alone, showing how a single supplier SDS and the fuller multi-notifier ECHA record can diverge; buyers should consult the specific supplier's current SDS before handling.
No US OSHA permissible exposure limit or ACGIH threshold limit value is published for ruthenium metal or its compounds, including RuO2, an absence rather than an oversight, unlike platinum, palladium and rhodium, which do carry federal exposure limits. RuO2 is not regulated as a dangerous good for DOT, IATA or IMDG transport and carries no UN number, unlike ruthenium(III) chloride and ruthenium tetroxide, which both do. ChemicalBook's safety data sheet also classes it as an oxidizer incompatible with organic solvents, aqua regia, acids and other oxidizers, and suppliers recommend storing it at 2 to 8°C, protected from light, under nitrogen.
Where Ruthenium(iv) oxide Chemistry Stops: Medical and Pharmaceutical Platinum#
This page covers ruthenium(iv) oxide strictly as an industrial electrode, electronics and catalysis material, not as a pharmaceutical agent. Platinum itself is the metal behind clinically used drugs such as cisplatin, but dosing, side effects and clinical protocols sit outside this site's chemistry-registry scope regardless of which platinum group metal is involved. Readers looking for platinum-based pharmaceutical content should consult a clinical source rather than this compound registry.
Related PGM Compounds#
Ruthenium(iv) oxide belongs to two overlapping families on this site: ruthenium's own compound network, and the platinum group metals' shared dioxide chemistry.
| Compound | Formula/composition | Relationship to ruthenium(iv) oxide |
|---|---|---|
| Ruthenium(iii) chloride | RuCl3, hydrate commercial form | Ruthenium's principal +3 salt; its hydrate is the universal precursor used to make RuO2 electrode inks |
| Ruthenium tetroxide | RuO4, CAS 20427-56-9 | The +8 ruthenium oxide; RuO4 reduces to RuO2 at a standard potential of +1.387 V, an electrochemical pair within the same oxide family |
| Ruthenium red | Trinuclear ruthenium ammine complex, CAS 11103-72-3 | A ruthenium ammine dye complex, structurally distinct but sharing the same metal |
| Tris(bipyridine)ruthenium(ii) chloride | C30H24Cl2N6Ru | A ruthenium(II) photoactive complex, contrasting with RuO2's simple binary +4 oxide structure |
| Platinum(iv) oxide | PtO2, CAS 1314-15-4 | Same rutile-family dioxide motif, different platinum group metal |
| Palladium(ii) oxide | PdO, CAS 1314-08-5 | A platinum group metal oxide at the +2 rather than +4 state |
| Iridium(iv) oxide | IrO2, CAS 12030-49-8 | The PEM-electrolyzer-grade acidic OER catalyst that displaces RuO2 where long-term stability, not activity, decides the choice |
| Osmium(iv) oxide | Osmium dioxide | Same +4 dioxide oxidation state, one row down the platinum group metal family |
History#
Ruthenium itself was discovered in 1844 by Karl Klaus, who isolated the element from platinum-ore refining residues at Kazan University, per PubChem's own element record; this corrects an earlier, less reliable 1827 attribution that this site's research process specifically checked and discarded. See ruthenium discovery and history for the full account. Ruthenium(iv) oxide itself rose to industrial importance a century later as the active coating of the dimensionally stable anode, the mixed-oxide-on-titanium electrode that completely displaced graphite anodes across the chlor-alkali industry, per this site's catalysis research.
Frequently Asked Questions#
What is ruthenium oxide? Ruthenium oxide most often means ruthenium(iv) oxide, RuO2 (CAS 12036-10-1), a dark blue-black, rutile-structured solid, 75.9% ruthenium by weight, used mainly as the active coating on dimensionally stable anodes for chlor-alkali electrolysis.
What is the crystal structure of RuO2? RuO2 crystallizes in the rutile-type tetragonal structure, space group P42/mnm (No. 136), with each ruthenium(IV) ion octahedrally coordinated by six oxide ions, per a 1997 neutron diffraction refinement in Acta Crystallographica B.
Is ruthenium a good catalyst? Yes. As RuO2, it is the most active oxygen-evolution electrocatalyst known, outperforming iridium(IV) oxide on activity, though it corrodes under the strongly acidic conditions of a PEM electrolyzer anode, which limits its acidic-OER role to milder chlor-alkali service.
What is ruthenium tetraoxide? Ruthenium tetroxide, RuO4 (CAS 20427-56-9), is a distinct, more highly oxidized ruthenium oxide, an extreme oxidizer used in organic synthesis rather than as an electrode material; it reduces to RuO2 at a standard potential of +1.387 V.
What is ruthenium mainly used for? Beyond RuO2's own DSA role, elemental ruthenium is used in the KAAP ammonia-synthesis process, Grubbs metathesis catalysts, platinum-ruthenium fuel cell anodes, hard-disk magnetic interlayers, thick-film chip resistors and as a promoter in the Cativa acetic acid process.